1. Field of the Invention
The present invention relates to a platen support for a hydraulic press, and more particularly to a square or rectangular shaped platen of large surface area.
2. Description of the Prior Art
A hydraulic press does useful work by applying pressure or force to material through means of a single or double acting hydraulic cylinder connected to a platen. The platen is sized according to the requirements of each individual press. During loading it can usually be expected that forces not on the platen geometric center will be encountered thus creating bending moments equal to the force times the distance to the geometric center. These bending moments are a major consideration in the press design as the press frame, cylinder rods, cylinder supports, as well as the platen, must structurally sustain the applied forces and bending moments due to off-centered loading. The bending moment becomes more significant as the platen surface area is increased.
A typical press design will have a single cylinder connected to the platen geometric center with the platen bending moments restrained by guides. For a square or rectangular platen, many presses use four round guides at each corner of the platen. These are typically precision machined to a good surface finish to allow bushings mounted on the platen to slide freely over the guides. The press frame is machined by boring in line the guide end connections and platen bushing connections so as to achieve the additional requirement that the guides be parallel with each other within the platen bushing clearance. Each guide must also be straightened within the platen bushing clearance or sized smaller to allow it to deflect as the platen moves on the guides. A means for guide lubrication is also required. This design has the disadvantage that the platen cannot easily be configured to enter an open top container such as a box.
Another typical design will use guides that move through the press frame within the area of the platen. For presses requiring precise platen movements these guides can be precision machined round rods that run through line bored bushings mounted on the press frame. The parallel and straightness requirements of the four post design above also apply to this design although as few as two guides may be used. For presses with less precise platen movements the guides may consist of greased slides that run over structural members such as channels or beams. Rollers are also used instead of slides depending on the particular application. The main purpose of the guides in either case is to restrain the bending moments generated by loading the platen off-center.
An improvement over the single cylinder design is noted in U.S. Pat. No. 4,273,037 which uses a cylinder at each end of the platen thus effectively reducing any moments encountered in the longitudinal axis of the platen. Moments perpendicular to this axis are again restrained by guides.
Many instances exist where the present invention offers advantages over press designs with the widely used moment restraining guides.